@topIndex: 2147483648;

html {height: 100%;}
#video {position:relative;z-index: 100;width:600px;height:400px;float: left;}
.test {width: 100px; height: 100px; background-color: red; color: #FFF; position: fixed; left: 50%; top:50%; margin-top: -50px; margin-left: -50px; z-index: @topIndex;}